Compound master cylinder



March 9, 1943i s, SCHNELL 2,313,274

COMPOUND MASTER CYLINDER Filed Oct. 8, 1941 INVEN TOR TE'VE SCHNELLPatentecl Man. 9, 1943 2,313,2=74 COMPOUND MASTER CLYLINDER SteveSchnell, Kirkwood, Mo., assignor to Wagner Electric Corporation, St.Louis, Mo., a corporation of Delaware Application October s, 1941,Serial N0. 414,087

8 Claims.

My invention relates to master cylinder devices for fluid pressureactuated ystems and more particularly I;o a compound master cylinderwhereby pressure created may be increase d without pro- ;iortionallygreater increase in the applied force.

One of thle objects of my invention is to construct; an improvedcompound master cylinder wherein the transition from the low pressureproducing means t9 the high pressure producing means may be efiected ina smooth manner.

Another object of my invention is I:o produce EI, simple and compactmaster cylinder device in which the low pressure and high pressureproducing pistons may be mounted in a single cylinder of uniformdiameter and wherein Ehe low pressure producing piston will be heldstation.rY when a predetermined pressure is developd thereby and thehigh pr8ssure producing piston will be capable ofindependent movement toproduce the high pressure.

Other objects of my invention will become apparent from the followingdes.cription taken in connection with I;he accompanying rawlng in whichI;he single figure is a sectional view of a compound master cYlinderdevice embodying my invention.

Referring to the drawing' in detail, the numeral I indicates a Casing inwhich is emboclied a reservoir 2 and a cylinder 3 of uniform internaldiameter. end of the .cylinder is provided with an outlet 4 connectedwith a branch condult 5 leading to a conduit 6 which is connected to thefluid motor (not shown) to be actuated by the developed fluid pressure.The outlet 4 has associated therewith a valve seat 1 with whichcooperates a valve element 8 biased onto said seat by a light spring 9.Becauseof this valve lt is seen that fluid may fiow. out of the forwardend of the cylinder I:o conduit 5 by unseating the valve element butfluid is prethe opposite direction.

The central part 'of the cylinder is also provided With an outlet Iwhich is connected by abranch conduit I I with the concluit 6.

Positioned within the real portion of the cylinder is a piston I2 havingan annular recess in order to form with the cylinder a chamber I3. Theretracted position of this piston is determined by stop I4 at the rearend 0f the cylinder. Associated With the rear end 0f the cylinder is 9.packing cup I for preventing the fluid from leaking out of chamber I3.The forward end of nisten I2 is provided with a cylinclrical extensionI6 which extends a considerable distance beis an annular member 24.

yond the head I'I of the piston. The piston head in the -skirl; also issealed by an annular packingcup I8 surrounding extention I6. The pistonI2, when in lts retract'ed position as shown, has 1ts head spacedconsiderably to the rear of outle t I0. The chamber I3 ab the rear ofthe head is in constant cQmmunication with the reservoir by an openingI9, and in order that fluid may freely pass the head o1? fihe piston andpacking cup I8 from chamber I3, the head is provicled with grooves 20.

A second piston 2I is positioned in'the forvvard portion of cylinder 3and carries'a packing cup 22. This second piston is provided with arearwardly extending skirt 23 'of than the cylinder and threaded intothe rear end Since skirt 23 is of smaller diameter than the cylinder,there is formed a chamber 25 surrounding the skirt between pistoh 2I andmember 24. The annular member 24 is adapted to receive the forward endof the projection I6 and in order 00 prevent the memberfrom sliding oftthe extension, said extension carries a washer 26 for.;engaging theinner end of the annular member. An annular packing cup 21 is associatedwith annular member 24 in order to seal it With the cylinder Wall andthe extension I 6. The annular member 24, together with the head I 'I'ofpiston I 2, the cylinder Wall and the extension I6, form amannular'chamber 28 which is in communicati;;nthe reserVoir by a p0rthole 29which 1s unc0vered when piston I2 is retracted.

The pistons 2I and I2 have interposgd therebetween a spring 30 ofpredeterniined strength said spring normally holding the pistons intheir extreme separated positions engagement of. washer 26 with theannular member 24. Thema is also provided a spring 3I which isinterposed between the end of the cylinder and piston 2I, this springbeing conslderably weaker than spring 30. In order that chamber 32 aheadof piston 2I may bein constant; communication with the reservoir whenthe piston 1s in retracted position there is provided a porthole 33positiqned just forward of the piston packlng cup when said piston isretracted. The reservoir is also in constant communication with theannular chamber 25 by an opening 34. An opening 35 permits interchangeof fiuid between chamber 25 and chamber 36 within the skirt'23 and theextension I6. In order to aid fiuid in passing the periphery of piston2I from chamber 25 saicl piston has its periphery provided with groqves3'I.

The pistons are actiiated by a piston rod 38 srnaller diameterdetermined by the from piston 2I.

cooperating with piston I2. A dust excluding boot 39 is associated withthe rear end cf the cylinder and the piston rod. Also, a light spring 4is interposed between annular cups I8 and 21 to hold these cups,respectively, against the Iaces of piston head I1 and annular member 24.

Rieferring to the operation, the parts of the master cylinder deVicewill be in the positions shown in Lhe figure when the master cylinder isinoperative, The reservoir will be filled with fluid as will alsochambers I3 28, 32. 25 and 36. When the mast-er cylinder is imperative,all these chaxrbers will be in cormnunication with ehe reservoir and,therefore, expansion and contraction of the fiuid will be freelypermitted.

When ii; is desired oo operate the master cylinder device to developfluid pressure, the pisison rod 23 is moved to the leih, thereby movingpis- Iaon I2. Due 150 the strength of spring 30, piston 2I will also bemoved to the leih simultaneously with piston I2. Initial movement ofpistons I2 and 2I will result in the por't-holes 29 and 33 being cut offby their respective packing cups I8 and 22. As soon as p0r'thole 33 iscut off, piston 2I will begin eo develop pressure in chamber 32 andfiuid will be forced out of the outlet 4 past valve element. 8 and intoehe brauch Conduit 5 and conduit Ii. The developed fluid pressure willalso be effective in chamb'@r 28 between the piston head I'l and theannular member 24 since this cha'mber is connected to conduit 6 bybrauch conduii: II and iI: cannot; expand.

When the pressure developed by piston 2| reaches a predeterminecl value,as determined by the strength of spring 30;- the spring will begin to becornpressed and ther(a will be relative movement between piston I2 andpisimn 2I. Due to this relative movement the chamber 28 will bedecreased in volume Iand I:he piston head I'I will begin todevelopadditional pressure and force fluid auf, thp outlet I0. Since this,additional pressure cannot, be effective in the chamber 32 ahead cfpiston 2I due to valve element 8, the pressure effective in the systemconnected to conduit 8 will now be solely controlled by piston I2. Thearea of piston head I'I, which is capable of daveloping pressure, issmaller than the pressure developing area o1 the piston head 2I and,thereiore, less actuating Iorce on the piscon rod 38 will be necessaryto produce the increase in pressureafter Spring 30 begins to becompressed. The

pistn 2l will no longer be moved i'orwardly since ans? piessure it i5capable of cleveloping will be less than that necessary to unseac valveelement 8 Which is held seated by the higher fluid pressure beingdeveloped by piston head I1 of pi ston I\2. As pistbn I2 movesrelatively to piston 2I, the Volume of chamber 38 will decrease but thefluid therein cah freely nass to the reservoir hroilgh chamber 25 andopening 34.

' When it is desired to release the developed -preS sure, piston rod 38will be permitted to be retracted. Spring 30 will now be free to expandand fluid under pressure can flow back into chamber 28 which willincrease in volume du e to Ehe relative movement betweg:n piston I2 awayWhen spring 30 has fully expanded and washer 25 becomes enaged with theannular member 24 on piston 2I, spring 3I will begin I:o expand andforce pistons 2I and I2 rearwardly as a unit. During the movement 01piston 2I rearWardly, fluid will flow from chamber 25 past the peripheryof piston 2I and the periphery o! cup 22 into chamber 32 to maintaint-his chamber filled w'1th fluid. When piston 7 2I reaches its fetractedposition, as shown in the figure, piston I2 will also reach itsretraoted position. Under thes conditions the 1301'th01e 29 will beuncovered to thlls release the remaining developed fiuid pressure inchamber 28 and the system conne0oed to conduii; S. If,during theretracting movement of piston I2 and priur 'i:o full expansion of spring30, there should be created a sub-atmospheric pressure in chamber 20 dueto slow return of developed pressure from the system, additional fluidmay fiow into said chember 28 irom chamber I3 by passing piston I1 andcup I8. y

If it is desired to release only a part of the developed fluid pressure,piston rod 38 is permitted to be partially retracted. This will permiteXpansion of chamber 28 and a decrease in the developed pressure.

When io is desired to employ the master cylinder device as a pump forblezading, the system connected to conduii; 6 is opened and then pistonrod 38 is moved forward. Pistons I2 and 2I will be moved as a unit andfluid forced out of chamher 32. The spring 30 will not be compressed asA no large pressure will be developed. When the piston rod is retractedand spring 3I pushes piston 2I rearwardly, fluid will flow into chamber32 from the reservoir by way of chamber 25 past the periphery 013 piston2 I Although I have shown a porthole 33 positioned ahead of the packingcup 22 when piston 2I is retracted in order to directly connect chamber32 to I:he reservoir, such porthole may be eliminated, if desired,without effecting the free expansion of fluid in chamber 32 whe thedevice is in operative. When porthole 33 is eliminated and fluid inchamber 32 expands, the pressure willbe relievedby way of valve 8,brauch conduits 5 and II, cliamber 28, and porthole 29 tothe reservoir.If the fluid in chamber 32 contr.cts, fiuid can by-pass the cup 22 fromthe reservoir by way oi opening 34.

Being aware of the possibility 01 modiflcations in the particularstructure herein describedwithout departing from the fundamentalprinciples o1! my invention, I do not intend that its scope be limitedexcept as, sei: forth by ihe appended claims.

Having iully described my invention, what I claim as new and desire tosecure by Lettersiatent of the United States is:

1. In iluid pressure producing afparatus aligned pistons havingdifferent pressure develop- -piscon of smaller area only until a.predetermined pressure is produced by the piston 01 larger area,

means for moving the piston 01 smaller area, outlets for placing saidchambers in communication with a device to be actuated, and. a. cheokvalve for preventing the fluld pressure developed by the piston 01smaller area from being efiective in the flrst chamber when said pistonoi smaller area is moved relatively to the piston o! larger area saidcheck valve being held closed by the iluid pressure developed by thepiston of smaller area to thereby prevent escape of fluid from the flrstchamber and maintain the pis'con oi larger area stationary.

2. In fiuid pressure producing apparatus, a sing1e cylinder of uniformdiameter, a piston in sa1d Ing the forward end o1 the cyllnder ahead o:th 'cylinder for producing a 1ow pressure, a second first plston und thechamber in communlcatlon p1stoninsaid cylinder,means forming an annularwlth a fluid pressure actuated devlce, am! a.. 1

cheunber and comprising an annular surface carcheck valve for prevenflng fiuld 1r0m floWing ried by the first piston and an annularsurface 5 from the chamber to the cy11nder ahead o1 the Y on sald secondpiston, a spring 015 predetermined first plston whexr' the se0nd plstondevelops strength between the pistons means for actuatpressure. l f

Ing the pistons slmultaneously through the spring. 6. In pressurep'roducing apparatus, a cylindgr an outlet frm the cylinder ahead of thefirst pisof-uniformlnternal dlameter, a. plston in the forton, an outletfrom the annular chamber, and ward part; o1 sald .cyllnder, an outletfrom the pressed, said second piston being movable relapositloned iniihe rer portlon of the cylinder tlvely to the first plston when heldstationary to 15 and provided wlth a cylindricalextemlon projecttherebydecrease the volume Qf the annular Ing through thg annular member saldsecond chamber and create a higher fiuid pressure tha.n piston' thecyllnder, the annular member and the I that developed by th e firstpiston'. extenslon fonnlng a pressure producing chamber 3. In fluidpressure prod ucing apparatus ema. spring of predetermlned strengthinterposed -b0dying 10W pressure producing means and high between theplstons, an o'utlet from the chamber, pressure producingmeans having a.Single cyllnand means for -placlng the two outlets In comder of uniformdiameter, said low pressure promunication with each other, said checkvalve duclng means comprising a piston in the forward Preventlng flow cffiuid from the chamber to end of the cylinder and said high pressureprothe forward end of the cyllnder. ducing means comprising mea)nsforming an an- 7. In pressure producing apparatus, a cyllnder ment Withrespect to the first piston, a spring o1! carrled by the rear of thepiston, a seond pisprisin g a check valve for causlng the flrst Pistenand the extension forming a pressurd productively to the first piston todecrease the vbluxne developed thereby is such tha.t the spring will belnterposed between the pistons, an outlet from compressed und theannula.r pistonfmoved relathe chamber. means for placing the two outletsin mxnunication with eac'h other, said check 01 the annular cha.mber. 40valve preventing flow of fluid from the chamber 4. In fluid pressureproducing apparatus emto the fTward end Qf the cylincler, a retractilebodying 1ow pressure producing means and h1gh spring for =the pistons,and means. for supplying 8 ec 131815011 P de W h n 11111111131 presbythe other plston, an actuatingmember for the y ment with spe t t t P s na p n of actuated member for Initial slmultaneous movepredeterminedstrength interposed between the the1'eby and compflsing spring of prgdg-D1St0IIS, 11189-115 atllting the Se00nd D I termined Strengthinterposedas an element beme s p s 01117 6 P rts o Dlac1ng the tween the me mbdarand the bi'ston of larger diam- 911d 15118 cylinder 811d 11118 niwl reter, separate outlets for placlng the chambers In strength lnte1posdvbetWeen the plstons, mea.ns 7

chamber in comn1unication wtlth 8. fiuid pressure communlcation with a.devlce to be actuated, und

actfl ed d vice an i a h k Valve p n a. check va.lve for preventing thefluid pressure 1ng fluid from fl0wlng t0 the forward end 0f e developedby the p1ston of smaller ar ea frorn be- Wunder .1Jhr0ugh the 17 6f- Drt thflref- 16 Ing eflectlve in the first .chamber when said pis- 5. Inpressureproducing appar tus, a cy lnder ton of smaller area 1s movedrelatlvely to the sitioned 111 S&ld cylinder rearwardly Of the fir'st tothereby prevenl; es(:ape o! fluld from the fifst for actuatlng thesecond pistqn, meazis for plac- ST SCH

